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Millwright Level 2 > Seals > Flashcards

Seals Flashcards

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1
Q

Seals used between two stationary parts

A

Static

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2
Q

Seals used between a moving and stationary part

A

Dynamic

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3
Q

Seals that prevent any fluid from leaking from one side of a system to the other

A

Positive

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4
Q

Seals which control the amount of leakage

A

Non-positive

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5
Q

All static seals are _______ seals

A

positive

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6
Q

These are installed at a joint between two stationary surfaces

A

Gaskets

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7
Q

List the common gasket and flange arrangements

A

Flat (full) face, raised face (ring), tongue and groove, Spigot and recess

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8
Q

This determines the number of bolts required

A

Thickness of joint material (thin flanges require more bolts)

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9
Q

What two things are gaskets made from?

A

metals and non metals

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10
Q

Inexpensive gasket, seals well against water, oil, and fuel

A

Paper (temp limit 120C/ 230F)

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11
Q

Gasket used in low-load applications, can be impregnated with an elastomer

A

Cork (-30 to 150C)

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12
Q

Gasket that has excellent mechanical properties and resists water and air

A

Natural Rubber (Upper temp limit 121C/ 250F)

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13
Q

Gasket used only for special applications such as high temps and steam turbines

A

Asbestos

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14
Q

Type of plastic gasket that resists heat, oil, and oxidation but does not perform well at low temps

A

Acrylic (Upper temp limit 232C / 450F)

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15
Q

Type of plastic gasket that is chemically inert, and performs well in extremely low temperatures

A

Teflon (-190 to 250C)

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16
Q

Types of gaskets that are harder and used in high pressure and high temp applications

A

Metallic gaskets (can be solid or composite of several materials)

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17
Q

The two types of circular gaskets

A

Ring style and Full face

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18
Q

Circular and made from synthetic rubber

A

O-rings

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19
Q

O-rings made from materials other than synthetic rubber have what?

A

manufacturers markings on them

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20
Q

Where are metallic o-rings used

A

extreme conditions of temperature, pressure, or corrosion

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21
Q

Shapes of o-rings used in hydraulic systems

A

Multi-lobed, square, rectangular

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22
Q

Compound often used in zero or low pressure applications

A

Sealants

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23
Q

Types of sealants

A

Non-hardening, hardening (flexible and rigid), tapes

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24
Q

Two categories of dynamic seals

A

contact and clearance

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25
Q

These seals make contact with the two surfaces to be sealed

A

Contact

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26
Q

These seals seal without touching each other

A

Clearance

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27
Q

Used as a non-positive seal to control leakage between stationary and moving parts

A

Packing (contact seal)

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28
Q

The three categories of packing

A

Compression, automatic, floating

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29
Q

Packing installed in the moving unit is called

A

inside-packed (cylinder pistons)

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30
Q

Packing installed the stationary unit is called

A

outside-packing (stuffing box)

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31
Q

Compression packing is made of these three classes of material

A

Fabric, metallic, plastic

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32
Q

Self lubricating packing is impregnated with this

A

graphite or teflon

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33
Q

This distributes sealing liquid under pressure to the packing

A

Lantern ring (seal cage)

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34
Q

What does 2-L-3-G indicate?

A

2 rings of packing, lantern ring, 3 rings of packing, gland

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35
Q

How should you stagger the ring joints?

A

90 degrees from each other

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36
Q

How far should the gland initially enter the stuffing box?

A

1/8” to 3/16”

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37
Q

How much should you tighten the gland bolts when initially installing?

A

a sixth of a turn, or one flat till desired leakage is reached

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38
Q

This packing uses system pressure to improve it’s sealing action

A

Automatic packing (V-ring, U-ring, O-rings, and cup packing)

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39
Q

What is balanced packing?

A

Seal on both the ID and OD (V-ring and U-ring)

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40
Q

What is unbalanced packing?

A

Seals on one diameter only (Cup packing)

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41
Q

V-ring packing is used in sets of how many?

A

3 or more

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42
Q

What must be used with V-ring packing?

A

internal and external adapter rings

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43
Q

How should V-ring packing sets used on double-acting pistons face

A

away from each other

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44
Q

One-piece molded ring with an endless design is meant to be used singly per seat, unlike v-ring packing

A

U-ring packing (less than 1500psi)

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45
Q

Only has one lip and is considered unbalanced

A

Cup packing

46
Q

An O-ring sits in a groove whose width is generally ___% to ___% of the O-rings cross section

A

135% to 150%

47
Q

The squeeze of an O-ring is equal to __% of ring diameter

A

10%

48
Q

What are standard O-rings rated to?

A

1500psi up to 3000psi using anti-extrusion rings or backup washers

49
Q

What are backup washers often made of?

A

leather, teflon, or moulded nylon

50
Q

This is a seal that is retained in a groove but not held in a static position. Seal by spring tension

A

Floating packing (ex. piston rings)

51
Q

Piston rings are what type of seal

A

non-positive

52
Q

Seal used in low pressure area (2 to 10psi)

A

Lip seals

53
Q

Materials used for lip seals

A

felt, leather, synthetic rubber

54
Q

The two types of lip seals

A

Single lip and double lip

55
Q

Type of ring seal used in high speed applications

A

Synthetic

56
Q

Non-positive seal which is mounted into a groove in the housing

A

Ring seals

57
Q

Non-positive seal that expels foreign material away, common on hydraulic and pneumatic cylinders

A

Wipers

58
Q

Positive seals used when it is vital no atmospheric contaminants reach working parts

A

Boots and bellows (Boots short bellows long)

59
Q

Positive seal which has a flexible membrane which spans between the stationary and moving parts

A

Diaphragm seals (flat and rolling)

60
Q

This seal is more effective than any other dynamic seals in preventing leakage

A

Mechanical seals

61
Q

This feeds the fluid into the product side of mechanical seals

A

flushing ports

62
Q

This prevents leakage of corrosive or toxic fluids into the atmosphere

A

Quenching

63
Q

Non-positive clearance seal mounted in s stationary housing. The simplest of seals

A

Bushings

64
Q

Non-positive clearance seal with a series of concentric or helical grooves in the housing bore

A

Annulus

65
Q

Non-positive clearance seal with a cupped washer-like flange, assists the sealing of a ring seal

A

Slinger seal

66
Q

Non-positive clearance seal with a tongue and groove design, uses a maze like path for foreign material to follow

A

Labyrinth seal

67
Q

This type of packing only seals in one direction

A

Automatic

68
Q

On centrifugal pumps and compressors roughly __% of the wear on the shafts is on the outermost rings closest to the gland

A

70%

69
Q

This packing type is very dense and works well in high pressure situations

A

Braid over braid

70
Q

Graphite ribbon that is wrapped around the shaft to form rings

A

Radial wound packing

71
Q

How should spiral wound packing be installed?

A

With the spiral orientated for shaft rotation

72
Q

What psi must the lantern ring receive to keep the pumping medium away from the packing?

A

approx 10-15psi

73
Q

What is the proper leakage rate for compression packing?

A

40 to 60 drops per minute

74
Q

Yarn used on rotating or reciprocating shafts and valves where high temperature must be taken into consideration

A

Carbon Yarn (up to 315C)

75
Q

Yarn with low coefficient of friction, excellent heat conductivity and chemical resistance.

A

Graphite yarn (up to 1925C)

76
Q

Fibre used in highly corrosive and oxidizing environments

A

PTFE Fibre (not exceed 260C)

77
Q

Refers to synthetic yarns and binders braided to form compression packing

A

Plastic packing

78
Q

Type of packing used in the form of foils or ribbons

A

Metal packing

79
Q

Fibre packing used to pump cold water, brine, or cold oil and can be used in marine applications

A

Vegetable fibre

80
Q

Shaft runout should not exceed

A

0.003”

81
Q

This type of gasket is commonly made of stainless steel, used for high-pressure and high temperature applications

A

Spiral-wound

82
Q

How do you calculate the the correct size of packing?

A

Subtract diameter of shaft from the OD of the stuffing box and divide by 2

83
Q

Cup packing is often replaced by this packing

A

U-ring (less maintenance time)

84
Q

The two types of diaphragm seals

A

Flat and rolling

85
Q

The primary seal in a mechanical seal is a _______ seal

A

dynamic

86
Q

The secondary seal in a mechanical seal is a ______ seal

A

static

87
Q

If the product discharge is used to flush it may have to go through this first

A

Cyclone strainer

88
Q

This braid packing is very flexible and commonly used for reciprocating applications

A

Square braid

89
Q

This braid packing is strong and resists being deformed or extruded under high pressures

A

Interlocking braid

90
Q

If the lantern ring is used to keep out harmful abrasives and chemicals it is most likely located where

A

at the bottom

91
Q

When are mechanical seals prohibited by law

A

When pump is used for fire safety

92
Q

How are mechanical seals classified

A

by arrangement and design

93
Q

How many seal points may be on a mechanical seal?

A

5 seal points

94
Q

This type of mechanical seal the mating faces do not actually come in contact

A

Gas-lubricated seals (0.0001”-0.0002” gap)

95
Q

In mechanical seals it is common practice to have the seal faces made of what?

A

Dissimilar metal (to prevent adhesion)

96
Q

This secondary seal is designed to push against a carbon face without breaking the primary seal

A

PTFE Wedges

97
Q

What are V-rings usually made of?

A

PTFE

98
Q

This secondary seal is pushed back and forth axially

A

Pusher seals

99
Q

The most commonly used pushing mechanisms in mechanical seals are

A

single spring and multiple spring

100
Q

Seal is used in conditions where no available metals can handle the mediums corrosive environment

A

PTFE Bellows seal

101
Q

Seals made up of a series of metal plates welded together

A

Welded metal bellow seals

102
Q

What are the two means of providing the drive for the rotating ring

A

mechanically or by friction

103
Q

These provide a cavity for holding and circulating a cooling or heating fluid near the seal

A

Gland jackets

104
Q

These are very common inside seals because of their higher seal face loading and less chance for leakage

A

Unbalanced seals

105
Q

These optimize seal face loading so that increases in hydraulic force are cancelled out

A

Balanced seals

106
Q

When are stationary seals used

A

When shaft speeds exceed 4500 ft/min

107
Q

These are often called environmental seals

A

Tandem mechanical seals

108
Q

Maximum tolerance for an adequate seal is considered this many light bands

A

3

109
Q

A seal on the bearing housing is called this

A

external seal

110
Q

A seal attached to the bearing is called this

A

integral seal

111
Q

A non pusher type seal is referred to as this

A

bellows

Millwright Level 2 (10 decks)

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